1. Field of the Invention
The present invention relates to a production method of a titanium-made plate-type heat exchanger.
2. Related Art
A conventional titanium-made plate-type heat exchanger is disclosed in Japanese laid open patent No.2002-35929. In the heat exchanger by this invention, herringbone patterned titanium plates are layered such that herringbone patterns of the neighboring plates are arranged in opposite directions each other, and first-fluid flow paths and second-fluid flow paths formed by gaps between the two neighboring plates are alternately arranged so that heat is exchanged between the two fluids.
The above-mentioned heat exchanger is produced according to the following steps: positions to be connected on respective herringbone plates are coated with or filled by a brazing solder; the coated or filled plates are placed in a vacuum heating furnace and the plates are degassed as reducing the pressure of the furnace and gradually raising the temperature of the furnace; and after a required reduced pressure is attained, coated or filled positions are brazed by heating the plates over 850° C.
However, the conventional titanium-made plate-type heat exchanger has the following problems.    (1) Since herringbone patterns are formed by concave strips with a chevroned cross section, two neighboring plates are contacted on concave edge points of respective concave strips crossing each other. Consequently, connected positions by the brazing solder show a point to point connection pattern so that a connected strength between the neighboring plates is low. As a result, a pressure-resistant performance of the flow paths of the heat exchanger is not so good.    (2) Since a heat transfer area of fluid flow paths formed by the two herringbone plates corresponds to surface areas of the herringbone plates, a heat transfer area per unit volume of the heat exchanger is not so large. Consequently, a heat radiating performance of the flow paths is not so good.    (3) When the plates are brazed at a temperature more than the transformation temperature (882° C.) of α-titanium, the herringbone plates are deteriorated, which means a durability of the heat exchanger is deteriorated.
And in producing the conventional titanium-made plate-type heat exchanger, since the herringbone plates are brazed over 850° C., they are deteriorated. Because when the brazing solder is heated over 850° C., sometimes the titanium-made plates are heated over the transformation temperature (882° C.) of α-titanium so that these plates are deteriorated.
The present invention is carried out in order to solve the problems mentioned above, and provides:    (1) A production method of a titanium-made plate-type heat exchanger having fluid flow paths with a pressure resistant performance, an excellent heat radiating performance and an excellent durability;    (2) A method to produce a titanium-made plate-type heat exchanger capable of preventing titanium members constituting the fluid flow path from deteriorating due to over-heating.